Solid state image pickup device

ABSTRACT

A solid state image pickup device is provided which includes: a semiconductor substrate having a light reception region; a well being formed in the semiconductor substrate; charge accumulation regions disposed in the well in a matrix shape; a vertical transfer channel disposed in the well; a light shielding film formed above the semiconductor substrate; and a horizontal transfer channel connected to the vertical transfer channels, wherein the light reception region includes: a first region in which an opening is formed through the light shielding film above each of the charge accumulation regions; a second region in which an opening is not formed through the upper light shielding film; and a third region defined between the first and second regions along the column direction of the charge accumulation regions, the third region not having at least partially the well and not having an opening formed through the upper light shielding film.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims priority of Japanese PatentApplication No. 2006-002447 filed on Jan. 10, 2006, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

A) Field of the Invention

The present invention relates to a solid state image pickup device, andmore particularly to a solid state image pickup device having an opticalblack region.

B) Description of the Related Art

With reference to FIGS. 3A to 3E, description will be made on thestructure of a CCD type solid state image pickup device. FIGS. 3A and 3Bare schematic plan views showing the structure of CCD type solid stateimage pickup devices, and FIG. 3C is a schematic plan view showing apartial area of a light reception region of a CCD solid state imagepickup device having a pixel interleaved array. FIG. 3D is a schematiccross sectional view showing a partial region of a light receptionregion of a CCD solid state image pickup device, and FIG. 3E is aschematic cross sectional view showing a partial region of a horizontaltransfer channel and a charge detection unit.

Reference is made to FIG. 3A. A CCD solid state image pickup device isconstituted of: a plurality of photosensitive regions 62 disposed, forexample, in a square matrix shape; a plurality of vertical transferchannels (vertical CCDs) 64 disposed along columns of the photosensitiveregions 62; a channel stop region 76 disposed between adjacent verticaltransfer channels 64; a horizontal transfer channel (horizontal CCDs) 66electrically connected to the ends of the vertical transfer channels 64outside a light reception region (pixel array region) 61; and a chargedetection unit 67 coupled to one end of the horizontal transfer channel66. The light reception region 61 is constituted of the photosensitiveregions 62 and vertical transfer channels 64.

The photosensitive region 62 is constituted of a photosensitive element,e.g., a photodiode, and a transfer gate. The photodiode generates andaccumulates signal charges corresponding to an incidence light amount.The accumulated signal charges are read to the vertical transferchannels 64 via transfer gates and transferred in the vertical transferchannels 64 along a direction (vertical direction, column direction)toward the horizontal transfer channel 66 as a whole. Signal chargestransferred to the ends of the vertical transfer channels 64 aretransferred into the horizontal transfer channel 66.

Signal charges transferred into the horizontal transfer channel 66 aretransferred in the horizontal transfer channel 66 along a directioncrossing the vertical direction as a whole, e.g., along a horizontaldirection (direction perpendicular to the vertical direction, rowdirection), and thereafter transferred to the charge detection unit 67.In accordance with the signal charges transferred from the horizontaltransfer channel 66, the charge detection unit 67 performscharges-voltage conversion and signal amplification. The amplified imagesignal is delivered to an external.

The array of photosensitive regions 62 includes a tetragonal array withthe photosensitive regions being disposed in a square matrix along therow and column directions at constant pitches as shown in FIG. 3A, andin addition, a pixel interleaved array (PIA) having pixels disposedalong the row and column directions by shifting the pixels, for example,a half pitch at every second rows and columns.

FIG. 3B is a schematic plan view of a CCD solid state image pickupdevice of the pixel interleaved array. The pixel interleaved array is anarray of photosensitive regions disposed in a first square matrix shapeand photosensitive regions disposed in a second square matrix shape atpositions between lattice points of the first square matrix shape. Thevertical transfer channel 64 is formed in a zigzag shape betweenphotosensitive regions 62. Also in this case, signal charges aretransferred in the vertical transfer channel 64 along a direction(vertical direction) toward the horizontal transfer channel 66 as awhole.

FIG. 3C is a schematic plan view showing some photosensitive regions ofa CCD type solid state image pickup device of a pixel interleaved array.A vertical transfer channel 64 is formed along a column of photodiodes60 disposed in a pixel interleaved array and in a zigzag shape betweenphotodiodes 60. A channel stop region 76 is formed between adjacentcolumns of vertical transfer channels 64. The channel stop region 76serves also as an isolation region between adjacent columns ofphotodiodes 60. Vertical transfer electrodes (a first layer verticaltransfer electrode 75 a and a second layer vertical transfer electrode75 b) are formed above the vertical transfer channels 64, covering thevertical transfer channels. Signal charges generated by photoelectricconversion of incidence light upon each photodiode 60 are read to theadjacent vertical transfer channel 64 when a read voltage is applied tothe first layer vertical transfer electrode 75 a. In FIG. 3C, thedirection of reading signal charges is indicated by arrows. Signalcharges read to the vertical transfer channel 64 are transferred in thevertical transfer channel 64 toward the horizontal transfer channel as awhole (along a downward direction in FIG. 3C).

FIG. 3D is a schematic cross sectional view showing a partial region ofthe light reception region of a CCD solid state image pickup device. Forexample, formed in a p-type well 82 (for example, constituted of a lowerlayer well p-type region 82 a and an upper layer well p⁻-type region 82b) formed in an n-type silicon substrate 81 with a high resistivityepitaxial layer are a charge accumulation region 71 made of an n-typeimpurity doped region and a vertical transfer channel 64 made of ann-type impurity doped region and being adjacent to a plurality of chargeaccumulation regions 71 and via an adjacent p-type transfer gate 72. Avertical transfer electrode 75 is formed above the transfer gate 72 andvertical transfer channel 64, with an insulating film 74 beinginterposed therebetween. A p-type or p⁺-type channel stopper region 76is formed between adjacent charge accumulation regions 71 and under thevertical transfer channel 64.

The channel stop region 76 electrically isolates the charge accumulationregion 71, vertical transfer channel 64 and the like. The insulatingfilm 74 is, for example, a lamination structure (ONO film) of an oxidefilm, a nitride film and an oxide film, formed on the surface of thesilicon substrate 81. The vertical transfer electrode 75 includes afirst vertical transfer electrode and a second vertical transferelectrode made of, for example, polysilicon. These electrodes may bemade of amorphous silicon. The vertical transfer electrode 75 controlsthe potentials of the vertical transfer channel 64 and transfer gate 72to read charges accumulated in the charge accumulation region 71 to thevertical transfer channel 64 and transfer the read charges in thevertical transfer channel 64 along the column direction.

An insulating silicon oxide film 77 is formed on the vertical transferelectrode 75, for example, by thermally oxidizing polysilicon.

A light shielding film 79 made of, for example, tungsten (W), is formedabove the vertical transfer electrode 75 via the insulating siliconoxide film 77 and an insulating film of silicon oxide, silicon nitrideor the like formed on the whole substrate surface by CVD or the like. Anopening 79 a is formed through the light shielding film 79 above thecharge accumulation region 71. The light shielding film 79 preventsincidence light upon the light reception region 61 from entering theregion other than the charge accumulation region 71. A silicon nitridefilm 78 is formed on the light shielding film 79. The silicon nitridefilm 78 is not necessarily required.

A planarizing layer 83 a made of, for example, boro-phospho silicateglass (BPSG) is formed above the light shielding film 79. A color filterlayer 84 of, e.g., three primary colors of red (R), green (G) and blue(B) is formed on the flat surface of the planarizing layer. In order toplanarize the upper surface of the color filter layer, anotherplanarizing layer 84B is formed. Micro lenses 85 are formed on a flatsurface of the planarizing layer 84B, for example, by melting andsolidifying a micro lens photoresist pattern. The micro lenses 85 are anarray of, e.g., fine semispherical convex lenses disposed above thecharge accumulation regions 71. Each micro lens 85 converges incidencelight on the charge accumulation region 71. Light converged by eachmicro lens 85 passes through the color filter layer 84 of one of red(R), green (G) and blue (B) and becomes incident upon the correspondingcharge accumulation region (photodiode) 71. A plurality of photodiodesinclude therefore three types of photodiodes: a photodiode upon whichlight transmitted through the red (R) color filter layer 84 becomesincident; a photodiode upon which light transmitted through the green(G) color filter layer 84 becomes incident; and a photodiode upon whichlight transmitted through the blue (B) color filter layer 84 becomesincident.

Signal charges accumulated in the charge accumulation region 71 andcorresponding in amount to an incidence light amount are read to thevertical transfer channel 64 by a drive signal (read voltage) applied tothe vertical transfer electrode 75 above the transfer gate 72, andtransferred in the vertical transfer channel 64 by a drive signal(transfer voltage) applied to the vertical transfer electrode 75.

A positive voltage is applied to the semiconductor substrate 81 as asubstrate drain voltage. Since the channel region 76 exists, a potentialbarrier between the charge accumulation region 71 and semiconductorsubstrate 81 is lower than a potential barrier between the verticaltransfer channel 64 and semiconductor substrate 81. Therefore, forexample, when excessive light enters the photodiode (charge accumulationregion 71), charges (electrons) overflowing from the charge accumulationregion 71 flow over the p-type barrier and into the n-type semiconductorsubstrate 81. This function is called a vertical type overflow drain(substrate drain shutter).

FIG. 3E is a schematic cross sectional view showing a portion of ahorizontal transfer channel and a charge detection unit of a CCD typesolid state image pickup device.

The n-type horizontal transfer channel 66 is formed, for example, in ap-type well 82 formed in a surface layer of an n-type semiconductorsubstrate 81. A first layer horizontal transfer electrode 87 and asecond layer horizontal transfer electrode 88 are alternately formedalong a longitudinal direction of the horizontal transfer channel 66above the horizontal transfer channel 66, with an insulating film 74being interposed therebetween.

A low impurity concentration region (n⁻type region) formed in a regionunder an area between adjacent first layer horizontal transferelectrodes 87 forms a reverse flow preventive potential barrier, and ann-type region between the n⁻type regions forms a potential well. Onetransfer stage is constituted of the potential well and the upstreamside (right side) potential barrier. As described earlier, the chargedetection unit 67 is formed at one end of the horizontal transferchannel 66.

The first layer horizontal transfer electrode 87 and second layerhorizontal transfer electrode 88 are connected in common at eachtransfer stage. In response to a drive signal (transfer voltage) appliedto the first layer horizontal transfer electrode 87 and second layerhorizontal transfer electrode 88, signal charges are transferred in thehorizontal transfer channel 66 along the horizontal direction toward theleft. The first layer horizontal transfer electrode 87 and second layerhorizontal transfer electrode 88 are made of polysilicon or amorphoussilicon.

The horizontal transfer channel 66 at the last transfer stage isconnected to a floating diffusion 90 of the charge detection unit 67 viaa transfer unit to which an output gate voltage VOG is applied. Signalcharges transferred in the horizontal transfer channel 66 aretransferred to the charge detection unit 67 (floating diffusion 90).

The charge detection unit 67 includes: the n⁺⁺-type floating diffusion90; an n-type reset gate RS 91, an n⁺⁺-type reset drain RD 93, a resetgate electrode 92 formed above the reset gate 91 with an insulating film74 being interposed therebetween; and an amplifier 94 having a MOStransistor whose gate is electrically connected to the floatingdiffusion 90. The reset gate electrode 92 is made of polysilicon oramorphous silicon.

Signal charges are transferred from the horizontal transfer channel 66to the floating diffusion 90. In the state when the floating diffusion90 is electrically isolated, charges-voltage conversion is performedbetween the transferred charges and a capacitance of the floatingdiffusion 90. A converted voltage signal is amplified by the amplifier94 and output as an image signal.

The signal charges transferred to the floating diffusion 90 are drainedto the reset drain 93 via the reset gate 91 after the charges-voltageconversion and before signal charges of the next pixel are sent to thecharge detection unit 67. A constant voltage φRG is applied to the resetgate electrode 92 for charge drain. With reference to FIGS. 4A to 4C,the light reception region (pixel array region) will be described morein detail.

FIG. 4A corresponds to FIGS. 3A and 3B and is a schematic plan viewshowing the structure of a CCD type solid state image pickup device.FIG. 4A does not show the photosensitive regions 62, vertical transferchannels (vertical CCDs) 64 and channel stop regions 76 shown in FIGS.3A and 3B.

As shown in FIG. 4A, a light reception region (pixel array region) 61 isconstituted of an effective pixel region 58 and an optical black region59. The effective pixel region 58 is defined in a non-peripheral area(central area) of the light reception region (pixel array region) 61,for example, as a rectangular area. The optical black region 59 isdefined in a peripheral area of the light reception region (pixel arrayregion) 61, surrounding the effective pixel region 58.

FIG. 4B is a cross sectional view taken along line 4B-4B of FIG. 4A,assuming that FIG. 4A is a plan view of an inter-line transfer typesolid state image pickup device such as shown in FIG. 3A. FIG. 4B ispartially simplified more than the cross sectional view of FIG. 3D.

As described earlier, the light reception region (pixel array region) 61includes the effective pixel region 58 and optical black region 59. Inboth regions, charge accumulation regions 71, vertical transfer channels64 and channel stop regions 76 are formed in a well 82 formed in asemiconductor substrate 81, and vertical transfer electrodes 75, asilicon oxide film 77 and a light shielding film 79 are formed above thesemiconductor substrate 81 formed with an insulating film 74.

In the effective pixel region 58, an opening 79 a is formed through thelight shielding film 79 above the charge accumulation region 71, whereasin the optical black region 59, no opening 79 a is formed through thelight shielding film 79 (the light shielding film 79 covers a regionabove the charge accumulation region 71).

FIG. 4C is a cross sectional view taken along line 4B-4B of FIG. 4A,assuming that FIG. 4A is a plan view of a pixel interleaved array typesolid state image pickup device such as shown in FIG. 3B.

A different point of FIG. 4C from the cross sectional view shown in FIG.4B resides in that the vertical transfer channel 64 under the verticaltransfer electrode 75 is divided into two regions by the channel stopregions 76. Also in the pixel interleaved array type solid state imagepickup device, the effective pixel region 58 differs from the opticalblack region 59 in that the opening 79 a is formed through the lightshielding film 79 above the charge accumulation region 71.

In the optical black region 59, incidence light is shielded by the lightshielding film 79. Therefore, only dark noises are generally generatedin the photodiodes or vertical transfer channels 64 in the optical blackregion 59, and these dark noises are a signal in the optical blackregion 59. A normal output signal in the effective pixel region 58 oftenadopts a value of a signal obtained in the effective pixel region 58subtracted by a black reference signal (i.e., dark noises) which is asignal in the optical black region 59.

Signal charges will not enter usually the optical black region 59 fromthe effective pixel region 58. This is because there is theabove-described vertical type overflow drain function.

However, when very strong light becomes incident upon the region of theeffective pixel region 58 near the optical black region 59, in somecases, electrons generated in the well 82 through photoelectricconversion are not drained to the n-type semiconductor substrate 81 butdiffuse and leak into the vertical channels 64 in the optical blackregion 59. Particularly, while a read pulse voltage is applied to thetransfer gate to read signal charges from the charge accumulation region71 to the vertical transfer channel 64, a potential under the electrodeapplied with the read voltage becomes lower than the potential at thevertical type overflow drain structure. It can therefore be consideredthat the vertical type overflow drain does not function sufficiently andleak of charges into the optical black region 59 occurs more likely (forexample, refer to JP-A-2003-224255).

Leak of charges into the optical black region 59 results in a lowersignal in the effective pixel region 58 and may corrupt a photographedimage, because the black reference signal contains the leak componentsin addition to the dark noises when the normal output signal in theeffective pixel area 58 is calculated.

Although pixels are made fine in recent years, a transmission depth oflight into silicon will not change. It is not easy to control motion ofcarriers generated at a deep position. Therefore, the above-describeddisadvantages occur more likely as solid state image pickup devices aremade more compact.

SUMMARY OF THE INVENTION

An object of this invention is to provide a solid state image pickupdevice capable of photographing a good quality image.

According to one aspect of the present invention, there is provided asolid state image pickup device comprising: a semiconductor substrate ofa first conductivity type having a light reception region defined in thesemiconductor substrate; a well of a second conductivity type oppositeto the first conductivity type, the well being formed in thesemiconductor substrate; a plurality of charge accumulation regions ofthe first conductivity type disposed in the well in the light receptionregion in a matrix shape, the charge accumulation region storing signalcharges generated in correspondence to an amount of incidence light; avertical transfer channel of the first conductivity type disposed in thewell in the light reception region along each column of the chargeaccumulation regions disposed in the matrix shape, the vertical transferchannel transferring signal charges accumulated in and read from thecharge accumulation regions along a column direction; a light shieldingfilm formed above a surface of the semiconductor substrate in an areaincluding the light reception region; and a horizontal transfer channelof the first conductivity type formed in the well and connected to endsof the vertical transfer channels, the horizontal transfer channeltransferring the signal charges transferred from the vertical transferchannels along a row direction, wherein the light reception regioncomprises: a first region in which an opening is formed through thelight shielding film above each of the charge accumulation regions; asecond region in which an opening is not formed through the upper lightshielding film; and a third region defined between the first and secondregions along the column direction of the charge accumulation regions,the third region not having at least partially the well and not havingan opening formed through the upper light shielding film.

According to another aspect of the present invention, there is provideda solid state image pickup device comprising: a semiconductor substrateof a first conductivity type having a light reception region defined inthe semiconductor substrate; a well of a second conductivity typeopposite to the first conductivity type, the well being formed in thesemiconductor substrate; a plurality of charge accumulation regions ofthe first conductivity type disposed in the well in the light receptionregion in a matrix shape, the charge accumulation region storing signalcharges generated in correspondence to an amount of incidence light; avertical transfer channel of the first conductivity type disposed in thewell in the light reception region along each column of the chargeaccumulation regions disposed in the matrix shape, the vertical transferchannel transferring signal charges accumulated in and read from thecharge accumulation regions along a column direction; a light shieldingfilm formed above a surface of the semiconductor substrate in an areaincluding the light reception region; and a horizontal transfer channelof the first conductivity type formed in the well and connected to endsof the vertical transfer channels, the horizontal transfer channeltransferring the signal charges transferred from the vertical transferchannels along a row direction, wherein the light reception regioncomprises: a first region in which an opening is formed through thelight shielding film above each of the charge accumulation regions; asecond region in which an opening is not formed through the upper lightshielding film; and a third region defined between the first and secondregions along the column direction, the third region not formed with thecharge accumulation regions and the vertical transfer channels and nothaving an opening formed through the upper light shielding film.

A solid state image pickup device can be provided which can photograph agood quality image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view showing the structure of a CCD typesolid state image pickup device according to an embodiment, and FIGS. 1Band 1C are cross sectional views taken along line 1B-1B shown in FIG.1A.

FIGS. 2A to 2D are schematic plan views showing modifications of theembodiment.

FIGS. 3A and 3B are schematic plan views showing the structure of CCDtype solid state image pickup devices, FIG. 3C is a schematic plan viewshowing a partial area of a light reception region of a CCD solid stateimage pickup device having a pixel interleaved array, FIG. 3D is aschematic cross sectional showing a partial region of a light receptionregion of a CCD solid state image pickup device, and FIG. 3E is aschematic cross sectional view showing a partial region of a horizontaltransfer channel and a charge detection unit of a CCD type solid stateimage pickup device.

FIGS. 4A to 4C are diagrams illustrating a light reception region (pixelarray region) more in detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a schematic plan view showing the structure of a CCD typesolid state image pickup device according to the embodiment, and FIGS.1B and 1C are cross sectional views taken along line 1B-1B shown in FIG.1A.

The CCD type solid state image pickup device of the embodiment ischaracterized in the structure of the optical black region shown inFIGS. 4A to 4C, and the other structures adopt the structures similar tothose described with reference to FIGS. 3A to 3E.

Reference is made to FIG. 1A. FIG. 1A is a plan view corresponding toFIGS. 3A and 3B. FIG. 1A does not show the photosensitive regions 62,vertical transfer channels (vertical CCDs) 64 and channel stop regions76 shown in FIGS. 3A and 3B. In FIG. 1A, the up/down (longitudinal)direction of the drawing is a vertical direction (column direction), andphotosensitive regions are formed along the up/down direction and aright/left direction (lateral direction, row direction) in the drawing.Vertical transfer channels are formed along the up/down direction in thedrawing in the case of a tetragonal array, and along the up/downdirection in a zigzag shape in the drawing in the case of a pixelinterleaved array.

A rectangular light reception region (pixel array region) 61 constitutedof photosensitive regions, vertical transfer channels (vertical CCDs)and the like includes an effective pixel region 58, an optical blackregion 59 and a well-less region 95. A size of the light receptionregion (pixel array region) 61 is, for example, 4100 μm in alongitudinal direction and 5500 μm in a lateral direction, although thesize changes depending upon a cell pitch and the number of pixels.

The effective pixel region 58 is defined in a non-peripheral area(central area) of the light reception region (pixel array region) 61,for example, as a rectangular area. In the effective pixel region 58, anopening is formed through the light shielding film above the chargeaccumulation region. A size of the effective pixel region 58 is, forexample, 4080 μm in a longitudinal direction and 5400 μm in a lateraldirection.

The optical black region 59 includes an evaluation region 59 a forevaluating leak light and the like and a black reference signalmeasurement region 59 b for measuring a black reference signal, and isformed surrounding the effective pixel region 58. In the optical blackregion 59, an opening is not formed through the light shielding filmabove the charge accumulation region (the light shielding film covers aregion above the charge accumulation region). As will be laterdescribed, it is not necessarily required that the optical black region59 is formed surrounding the effective pixel region 58.

In the solid state image pickup device of the embodiment, the evaluationregion 59 a is formed at a position adjacent to the effective pixelregion 58 along the longitudinal direction. The black reference signalmeasurement region 59 b is formed on the right side end (on the sideopposite to the side where the charge detection unit 67 is formed, onthe upstream side along the horizontal direction) of the light receptionregion (pixel array region) 61 along the longitudinal direction.

The well-less region 95 is formed between the evaluation region 59 a andblack reference signal measurement region 59 c along the verticaldirection. The light shielding film without opening is formed above thewell-less region 95.

FIG. 1B is a cross sectional view taken along line 1B-1B of FIG. 1A,assuming that FIG. 1A is a plan view of an inter-line type solid stateimage pickup device such as shown in FIG. 3A. FIG. 1B is partiallysimplified more than the cross sectional view of FIG. 3D.

The light reception region (pixel array region) 61 includes theeffective pixel region 58, optical black region 59 and well-less region95. In the effective pixel region 58 and optical black region 59, chargeaccumulation regions 71, vertical transfer channels 64 and channel stopregions 76 are formed in a well 82 formed in a semiconductor substrate81. Vertical transfer electrodes 75, a silicon oxide film 77 and thelight shielding film 79 are formed above the semiconductor substrate 81with an insulating film 74 formed on the surface thereof.

Of the optical black region 59, the evaluation region 59 a is formedadjacent to the effective pixel region 58 and constituted of photodiodes(charge accumulation regions 71) of at least one column.

The well-less region 95 is formed adjacent to the evaluation region 59 aand has a width of, e.g., 3 to 15 μm. In the well-less region 95, thewell 82 is not formed in the semiconductor substrate 81. Impurity dopedregions are neither formed, such as the charge accumulation region 71,vertical transfer channel 64, channel stop region 76 and the like.

Of the optical black region 59, the black reference signal measurementregion 59 b is a region defined adjacent to the well-less region 95 andon the upstream side in the horizontal direction.

FIG. 1C is a cross sectional view taken along line 1B-1B of FIG. 1A,assuming that FIG. 1A is a plan view of a pixel interleaved array typesolid state image pickup device such as shown in FIG. 3B.

A different point of the cross sectional view of FIG. 1C from the crosssectional view of FIG. 1B resides in that the vertical transfer channel64 under the vertical transfer electrode 75 is divided into two portionsby the channel stop regions 76.

As shown in FIGS. 1A to 1C, the following advantages are obtained byforming the evaluation region 59 a, black reference signal measurementregion 59 b and well-less region 95.

First, in the well-less region 95, the p-type well 82 is not formedwhich otherwise forms a potential barrier along the direction toward thesemiconductor substrate 81. Namely, in the well-less region 95, abarrier along a depth direction of the semiconductor substrate 81 is notformed or is very low, and a low potential region relative to electronsis formed through the semiconductor substrate 81 along the depthdirection. It is therefore possible to drain charges entered thewell-less region 95 to the semiconductor substrate 81 side easily.Accordingly, even if charges are diffused in response to incidence ofstrong light upon the effective pixel region 58 near the evaluationregion 59 a, the diffused charges are drained to the semiconductorsubstrate 81 in the well-less region 95. It is possible to preventcharges from entering the optical black region 59 (black referencesignal region 59 b) on the more upstream side than the well-less region95 in the horizontal direction. A correct black reference signal cantherefore be measured in the black reference signal measurement region59 b. This is also applicable to the case in which the vertical typeoverflow drain does not function sufficiently (the case in which a readpulse voltage is applied to the transfer gate to read signal chargesfrom the charge accumulation region to the vertical transfer channel).

The evaluation region 59 a is a region for evaluating an influencedegree of the effective pixel region 58. By comparing a charge amountmeasured in the black reference signal measurement region 59 b with acharge amount measured in the evaluation region 59 a, it becomespossible to detect and evaluate a charge leak amount from the effectivepixel region 58 such as smear and blooming. It is also possible toevaluate a charge transfer efficiency in the horizontal transferchannel.

The present inventors manufactured CCD type solid state image pickupdevices (pixel interleaved array type solid state image pickup devices)of the embodiment and conducted experiments. Even if a high luminancetarget image such as the Sun was photographed, a lowered or reducedsignal in the effective pixel region 58 was able to be suppressed and agood quality image was obtained. It has been found that the suppressioneffect depends on the width of the well-less region 95 and thesuppression effect becomes larger as the width is wider.

The present invention has been described in connection with thepreferred embodiment. The invention is not limited only to the aboveembodiment.

FIGS. 2A to 2D are schematic plan views showing modifications of theembodiment.

For example, as shown in FIGS. 2A and 2B, the optical black region 59 isnot necessary to be formed surrounding the effective pixel region 58.

Further, as shown in FIG. 2C, the well-less region 95 may be formed at aposition adjacent to the effective pixel region 58, without forming theevaluation region 59 a.

Furthermore, as shown in FIG. 2D, wells may be formed in some regions ofthe well-less region 95. In FIG. 2D, the regions where wells are formedare well formed regions 95 a indicated by hatching.

In this specification, although the optical black region 59 andwell-less region 95 have been described discretely, the well-less region95 may be considered as a portion of the optical black region 59.

It will be apparent to those skilled in the art that other variousmodifications, improvements, combinations, and the like can be made.

The present invention is applicable to CCD type solid state image pickupdevices.

1. A solid state image pickup device comprising: a semiconductorsubstrate of a first conductivity type having a light reception regiondefined in said semiconductor substrate; a well of a second conductivitytype opposite to said first conductivity type, said well being formed insaid semiconductor substrate; a plurality of charge accumulation regionsof said first conductivity type disposed in said well in said lightreception region in a matrix shape, said charge accumulation regionstoring signal charges generated in correspondence to an amount ofincidence light; a vertical transfer channel of said first conductivitytype disposed in said well in said light reception region along eachcolumn of said charge accumulation regions disposed in said matrixshape, said vertical transfer channel transferring signal chargesaccumulated in and read from said charge accumulation regions along acolumn direction; a light shielding film formed above a surface of saidsemiconductor substrate in an area including said light receptionregion; and a horizontal transfer channel of said first conductivitytype formed in said well and connected to ends of said vertical transferchannels, said horizontal transfer channel transferring said signalcharges transferred from said vertical transfer channels along a rowdirection, wherein said light reception region comprises: a first regionin which an opening is formed through said light shielding film aboveeach of said charge accumulation regions; a second region in which anopening is not formed through said upper light shielding film; and athird region defined between said first and second regions along thecolumn direction of said charge accumulation regions, said third regionnot having at least partially said well and not having an opening formedthrough said upper light shielding film.
 2. The solid state image pickupdevice according to claim 1, wherein said light reception region furthercomprises a fourth region defined between said first and third regionsalong the column direction of said charge accumulation regions, saidfourth region including said vertical transfer channel of at least onecolumn and not having an opening formed through said upper lightshielding film.
 3. The solid state image pickup device according toclaim 1, wherein said third region is not formed with said chargeaccumulation regions and said vertical transfer channels.
 4. The solidstate image pickup device according to claim 1, wherein said firstconductivity type is an n-type.
 5. A solid state image pickup devicecomprising: a semiconductor substrate of a first conductivity typehaving a light reception region defined in said semiconductor substrate;a well of a second conductivity type opposite to said first conductivitytype, said well being formed in said semiconductor substrate; aplurality of charge accumulation regions of said first conductivity typedisposed in said well in said light reception region in a matrix shape,said charge accumulation region storing signal charges generated incorrespondence to an amount of incidence light; a vertical transferchannel of said first conductivity type disposed in said well in saidlight reception region along each column of said charge accumulationregions disposed in said matrix shape, said vertical transfer channeltransferring signal charges accumulated in and read from said chargeaccumulation regions along a column direction; a light shielding filmformed above a surface of said semiconductor substrate in an areaincluding said light reception region; and a horizontal transfer channelof said first conductivity type formed in said well and connected toends of said vertical transfer channels, said horizontal transferchannel transferring said signal charges transferred from said verticaltransfer channels along a row direction, wherein said light receptionregion comprises: a first region in which an opening is formed throughsaid light shielding film above each of said charge accumulationregions; a second region in which an opening is not formed through saidupper light shielding film; and a third region defined between saidfirst and second regions along the column direction, said third regionnot formed with said charge accumulation regions and said verticaltransfer channels and not having an opening formed through said upperlight shielding film.